1. Field
The disclosure relates to a method for producing soft magnetic strip material, especially a method for producing soft magnetic strip material for roll tape-wound cores and a device for carrying out the method.
2. Description of Related Art
Soft magnetic material is used in different applications. Thus, for example, it is used in the form of strips of nanocrystalline alloys in wound magnetic cores, so called annular tape-wound cores that are used, i.a., in current transformers, power transfer systems and power inductors as well as magnetic converter heads or current converter cores. Various production methods and the pertinent production devices are known for producing the soft magnetic material.
The known production devices are generally made as continuous annealing systems and enable heat treatment of rapidly solidified magnetic material (hereinafter “tape material”). The rapidly solidified magnetic material is produced by a casting process and then wound into a roll in order to then be fed as a continuous tape into the continuous annealing system and to be processed by the latter to form a soft magnetic material. Within the scope of processing, the material is heat-treated and at the same time placed under tensile stress to obtain the desired magnetic properties of the tape.
U.S. Pat. No. 6,171,408 B1 describes a corresponding production method for annular tape-wound cores that consist of amorphous ferromagnetic material. The method calls for casting an amorphous ferromagnetic tape that is then moved through a heated environment and is at the same time exposed to a magnetic field. The speed of movement is matched to the heated environment such that defined heating of the tape for a defined time interval takes place.
A production device that can be used for this method is described in, for example, U.S. laid-open specification US2008/0196795A1. The device comprises a work-holding spindle for holding a tape coil of amorphous cast tape material. The device furthermore comprises a temperature-controlled, tunnel-shaped furnace for producing a nanocrystalline strip from the amorphous tape material and at least one S-shaped unit that is located upstream from one entrance of the tunnel-shaped furnace for the tape material and is connected to a braking motor and a clamping device for setting the tensile force in the longitudinal direction of the amorphous tape material. A control apparatus in conjunction with a dynamometer controls the braking motor of the S-shaped unit located upstream from the entrance of the tunnel-shaped furnace.
In addition, there is a second S-shaped unit that is located following an exit of the tunnel-shaped furnace and is connected to a motor. The device, moreover, has a winding mandrel for the nanocrystalline strip produced for manufacturing a magnetic core of nanocrystalline material. Using this device, the amorphous tape material that has been wound into a coil on the work-holding spindle is again unwound from the latter and passes through the first S-shaped unit located upstream from the entrance of the tunnel-shaped furnace, then the dynamometer and the following tunnel-shaped furnace before it passes the second S-shaped unit located at the exit of the tunnel-shaped furnace and is wound on the following winding mandrel as described above to form the magnetic core.
One example of a magnetic core wound in this way from nanocrystalline material is also known from U.S. Pat. No. 7,583,172 B2. This core is used, i.a., in current sensors and should have permeability that is as low as possible in this respect for purposes of sufficient measuring accuracy.
The known devices and production methods therefore call for the amorphous tape material that is to be processed to be placed under tensile stress during heat treatment. In this way, via the prevailing tensile stress, anisotropy in the tape material can be induced so that the soft magnetic strip material produced from it has a pronounced flat hysteresis loop with a defined permeability μ (according to the induced anisotropy) along the direction of the tensile stress since a permeability level that can be achieved within the scope of the described production method is dependent on the applied tensile stress.